A liquid crystal display device is widely used for a display of a personal computer, a television and so forth. The device utilizes optical anisotropy, dielectric anisotropy and so forth of a liquid crystal compound. As an operating mode of the liquid crystal display device, a variety of modes are known, such as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the IPS mode, the FFS mode and the VA mode are known to improve narrowness of an angle of visibility, which is a disadvantage of operating modes such as the TN mode and the STN mode. In the liquid crystal display device having the mode of the kind, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the liquid crystal display device, a liquid crystal compound contained in the composition preferably has physical properties described in items (1) to (8) below.                (1) High stability to heat, light and so forth,        (2) a high clearing point,        (3) a low minimum temperature of a liquid crystal phase,        (4) a small viscosity (η),        (5) a suitable optical anisotropy (Δn),        (6) a large negative dielectric anisotropy (Δ∈),        (7) a suitable elastic constant (K33: bend elastic constant), and        (8) an excellent compatibility with other liquid crystal compounds.        
An effect of physical properties of the liquid crystal compound on the characteristics of the device is as described below. A compound having a high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes longer. A compound having a high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having a low minimum temperature of the liquid crystal phase such as a nematic phase and a smectic phase, as described in (3), in particular, a compound having a low minimum temperature of the nematic phase, also extends a temperature range in which the device can be used. A compound having a small viscosity as described in (4) decreases a response time of the device.
A compound having a suitable optical anisotropy as described in (5) improves a contrast of the device. In accordance with a design of the device, a compound having a large optical anisotropy or a small optical anisotropy, mare specifically, a compound having a suitable optical anisotropy, is required. When decreasing the response time by decreasing a cell gap of the device, a compound having a large optical anisotropy is suitable. A compound having a large negative dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device is decreased.
With regard to (7), a compound having a large elastic constant decreases a response time of the device. A compound having a small elastic constant decreases the threshold voltage of the device. Therefore, a suitable elastic constant is required according to characteristics that are desirably improved. A compound having an excellent compatibility with other liquid crystal compounds as described in (8) is preferred because physical properties of a composition are adjusted by mixing a liquid crystal compound having different physical properties.
A variety of liquid crystal compounds having a negative dielectric anisotropy have so far been prepared (for example, patent literature Nos. 1 to 3). Patent literature No. 1 discloses compound (A). Patent literature No. 2 discloses compound (B) and compound (C). However, the compounds are not fully suitable for a mode of a liquid crystal display device in recent years.

Excellent physical properties that are not found in a conventional compound can be expected from a new compound. The new compound is expected to have a suitable balance between two physical properties required upon preparing a liquid crystal composition. In view of such a situation, development is desired for a compound having excellent physical properties and a suitable balance between the physical properties with regard to (1) to (8) as described above.